Deleterious effects of bridging ??

IMHO, I'm not sure the NAD advice is correct above. If the 370 and 270 offer the same output power you should be ok and better off. I can't offer anyting re: Parasound vs NAD.

Bridging will obviously increase the power by a factor of three or four. However, it also increases the distortion and, in addition, limits the ability of the amplifier to drive lower impedance loads. With many bridged amplifiers, 8 ohms is the preferred load. However, with those precautions in mind, I have used bridged amplifiers several times in the past 36 years and never had a problem; and did in fact enjoy the markedly increased power delivery. Also keep in mind that the hook-up instructions for some bridged amps can be a bit tricky, so read the instructions very carefully.

Bridging will mean that because each "channel" of output is seeing only half of the loudspeaker load (the + or the - terminal), the amp will see the loudspeaker as half of its actual impedance if both channels were driving it. This means that if your Maggies are a nominal 4 ohm load, the amps will see them as nominal 2 ohm loads. This can strain the power supply, since it has to deliver a pretty healthy amount of current without any voltage increase. This is why higher impedance loudspeakers are a better match for bridging. Be careful to make sure that the amps are up to it, especially at higher listening levels. If the speaker dips lower at any point, you'll be straining the amps quite a bit.

I was told recently, by two knowledgable people, that bridging does in fact degrade an amp's damping factor. This is probably yet another case of "try it yourself to see what happens" esp. in light of positive experiences (ie: Hifiexpert) shared above.

Bridging does not result in seeing half the speaker impedance. There is no complete circuit to just the + or - terminal. Bridging puts the outputs of the two amps in series, effectively doubling the available output voltage swing. The same gain setting will result in supplying twice the current to the SAME load, if the amp has the current capability. That results in four times the power. That is why some mention the problem of an inherently low impedance speaker with the additional voltage swing of a bridged amp applied. Often the amp can not supply that much current. That is why 3 to 4 times the power is correctly claimed in a previous post. How much current does your speaker take to drive it to adequate listening levels and what is its nominal impedance? Does your unbridged have high enough voltage output to drive it to that level? Those are the questions. If it doesn't play loud enough and the amp is voltage limiting, then bridging is a possible solution. If it doesn't play loud enough and the amp is current limiting, then you need a higher current supplying amp or a more efficient speaker. Bridging won't help because if the amp is current limiting unbridged, it will just limit at a lower gain setting when bridged. I know, a lot of words, but there are 3 current threads on bridging and a lot of misunderstanding. See BIAMPING under Speakers, for example (it includes bridging). :)